• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.5
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• pp.383-389
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• 2000

The relationship between the DC degradation characteristics of the ZnO varistor and the ambient sintering-process is investigated in this study. ZnO varistors made o matsuoka’s composition were fabricated by standard ceramic techniques. The ambient sintering-process is performed at the extraordinary electrical-furnace which is equipped with the vacuum system. Gases used in sintering process were oxygen nitrogen argon and air. Using XRD and SEM the phase and microstructure of samples were analyzed respectively. The conditions of DC degradation tests were conducted at 115$\pm$2$^{\circ}C$ for 13 h. Current-voltage analysis is used to determine nonlinear coefficients($\alpha$). Frequency analysis are performed to understand electrical properties as DC degradation test. From above analysis it is found that the ZnO varistor sintered in oxygen atmosphere showed superior properties at the DC degradation test and degradation phenomenon of ZnO varistor is caused by the change of electrical properties in grain boundary. These results are in accordance with Gupta’s degradation model.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.115-118
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• 2000

In case of developing new motor, many examinations was tested to decide a motor efficiency and reliability. To give reliability judgment, traction motor winding insulation was tested by electrical method after appling electrical, heat, mechanical, environmental stress. In this study, stator form-wound winding of traction motor in urban transit E.M.U was tested by accelerative thermal degradation test. Stator form-wound winding was tested on the accelerative degradation composed of heat, vibration, moisture, overvoltage and researched insulation resistance, dielectric loss, partial discharge for insulation degradation properties, evaluated withstand voltage. Degradation temperature was $230[^\circ{C}]$, $250[^\circ{C}]$, $270[^\circ{C}]$, for stator form-wound winding respectively. On the test results of accelerative thermal degradation, insulation properties were relied all temperature until 10 times and expected life was evaluated by the rule of reducing $10[^\circ{C}]$ life into halves. Expected life was 31.8 years. It is guaranteed insulation reliability because of exceeding 25 years life times as considering.

• Journal of Korean Society for Quality Management
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• v.35 no.4
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• pp.61-66
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• 2007

The performance of a building material degrades as time goes by and the failure of the material is often defined as the point at which the performance of the material reaches a pre-specified degraded level. Based on a stochastic deterioration model, a performance based service life prediction method for building materials and components is developed. As a stochastic degradation model, a gamma process is considered and lifetime distribution and service life of a material are predicted using the degradation model. A numerical example is provided to illustrate the use of the proposed service life prediction method.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.2837-2845
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• 1994

Several methods have been developed to predict on the remaining life of the old power plants. However, Larson-Miller parameter, one of existing creep life prediction methods, has not reflected the effect of material degradatioin and grain size. So this study has been carried out to research the effects of material degradation and austenite grain coarsening on the life prediction of 3.5Ni-Cr-Mo-V steel. An experimental result shows that carbide coarsening has no significant effects on the creep rupture life and the Larson-Miller parameter, but grain coarsening has an important influence on the creep ruptrure life and the Larson-Miller parameter. Therefore Larson-Miller constant, K should be determined to consider on the chemical composition and the grain size of materials.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.207-210
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• 2001

Electrical equipment for railway is always experiencing wear and degradation by mechanical, electrical and environmental stress in service and the fault or the accident of high voltage main circuit directly causes operation interruption. Particularly propulsion drive of high speed switching inverter takes the form of specific degradation mechanism such as fast rising transient surge, reflective overvoltage and harmonic stress, and it is known that it threatens the long life and the reliability of electrical equipment. In this paper, statistics of fault and accident on main electrical equipment for railway are presented and also insulation degradation mechanism, which governs end life of electrical device, is analyzed. Finally the method of fault respondence and reliability improvement on the main electrical equipments will be reviewed in order to prevent operation interruption.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.427-430
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• 2001

The degradation characteristics versus MgO Additive for the ZnO ceramic devices fabricated by the standard ceramic techniques is investigated in this study. It were made these devices be basic Matsuoka's composition. Especially, MgO were added to analyze the degradation characteristics and sintered in air at 1300$^{\circ}C$. The conditions of DC degradation test were 115${\pm}$2$^{\circ}C$ for 12h. Using XRD and SEM, the phase and microstructure of samples were analyzed respectively. The elemental analysis in the microstructures was used by EDS, E-J analysis was used to determine ${\alpha}$ . Frequency analysis was accomplished to understand the relationship between R$\sub$g/ and $R_{b}$ with the electric stress at the equivalent circuit.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.12
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• pp.1289-1295
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• 2004

In this paper, degradation in field-aged PV modules including degradation of interconnect, discoloration of encapsulant and hot spot have been observed and analyzed. From the results, photovoltaic module installed for 6 years shows around 16 % drop of electrical properties due to the interconnect degradation and PV module passed 18 years has been found to drop of around 20 % mainly by the encapsulant discoloration. Furthermore the difference between low and high temperature of PV array at hot spot goes up to 3$0^{\circ}C$ and it leads to interconnect degradation. On the other hands, the temperature difference was observed to be around 15$^{\circ}C$ at the encapsulant discoloration spot of PV array.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.04b
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• pp.49-52
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• 2002

Degradation characteristics of cathodoluminescence (CL) of ZnS:Ag,Cl phosphor were investigated with measurements of CL and photoluminescence (PL). Phosphoric acid treatment was performed to phosphor particles in order to improve CL degradation of phosphor screen that occurred during panel sealing process, and we will discuss mechanisms of degradation and improvement of luminescence mainly with help of AES (auger electron spectroscopy) analysis.

• Journal of the Korean Ceramic Society
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• v.49 no.1
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• pp.48-55
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• 2012

Degradation of performance and life time of a functional material or device thereof is induced, to a great extent, by mass transfer in the material that is driven by various thermodynamic forces imposed intentionally or accidentally during its operation or service. The forces are any gradient of intensive thermodynamic variables, component chemical potentials, electrical potential, temperature, stresses, and the like. This paper reviews electric-field induced degradation phenomena in ionic solid compounds including insulation resistance degradation, crystal shift, microstructural alterations, compositional unmixing, and compound decomposition. Their inner workings are also discussed qualitatively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.177-180
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• 2000

We studied the degradation of EVA for the protection of solar cell by UV-rays irradiation. We investigated the reduction of electrical efficiency, photo transmmitance and degradation of EVA by UV-rays irradiation. We utilized the UV irradiation equiped with fluorescent 313nm UV lamp and radiated for 400 hours. For the chemial analysis, we used the UV-vis spectrometer, XPS and examined the degradation mechanism by UV irradiation. It is found that the discolored phenomena, the decrease of photo transmmitance and oxidation reaction is occured by UV irradiation on the EVA sample for the protection of solar cell.